Bone screws are widely used to secure a fractured bone in place while the bone heals. For example, when a bone breaks, the two pieces of the broken bone usually become misaligned making it difficult for the bone to heal properly. Although a surgeon can manipulate the pieces of the broken bone back into alignment, there is a tendency for the pieces of bone to again become misaligned during the lengthy healing process due to movement by the patient. Surgeons therefore often use bone screws to screw the pieces of the broken bone together, reducing the likelihood that the bone pieces will move during the healing process.
In order to provide sufficient strength and support to keep the bone pieces in place while the bone heals, bone screws typically have diameters in excess of 4.5 millimeters. For example, the diameter of a bone screw commonly used to engage the cortical bone is 4.5 millimeters, while a 5.0 millimeter bone screw is used to engage the cancellous bone.
Due to the difficulty associated with placing such large diameter bone screws into a fractured bone, smaller diameter guide pins are used to initially immobilize the fractured bones, and to then guide the larger bone screws into place. One commonly used guide pin, having a diameter of about 2.0 millimeters, is illustrated in FIG. 1, and includes an elongated shaft or shank 12 (only a portion of which is shown in FIG. 1), a threaded portion 14 and a drill end 16.
A surgeon will first align the pieces of the fractured bone, and then screw the guide pin into the fractured bone using the drill end 16 and the threads 14 to advance the guide pin into the bone. A cannulated bone screw (i.e., a bone screw having a hollow center), with an inner diameter slightly larger than the diameter of the guide pin, is then placed over the guide pin, and is advanced along the guide pin toward the injured bone. When the bone screw reaches the bone, the bone screw is screwed into the bone, providing sufficient support for the bone to heal. Once the bone screw is in place, the guide pin is removed.
Therefore, the guide pin provides a guide for the movement of the bone screw and also serves to keep the bone pieces properly aligned while the bone screw is being screwed into the bone. Unfortunately, since the diameter of the guide pin is necessarily quite small, the forces exerted on the guide pin by the physician during placement of the guide pin, or subsequent placement of the bone screw, may cause the guide pin to fracture during the procedure at the point where the thread portion meets the shaft. The surgeon must then remove the broken pieces of the guide pin, and may need to begin the procedure again using a new guide pin.